The present invention relates to a call control system for an intelligent network (IN).
An intelligent network (IN) for future switch boards has been developed and is now under study by CCITT (Comite Consultatif International des Telegraphique et Telephonique). This intelligent network (IN) provides a switching technology for efficiently executing greatly expanded services in the future.
FIG. 1 shows a system architecture of a conventional intelligent network (IN).
As shown in FIG. 1, a service control device (SCP: Service Control Point) 101 is provided to control a variety of services provided by the intelligent network (IN). The SCP 101 is connected to a telephone signal network 102 to bring services to subscriber terminals, which belong to the telephone signal network 102. The telephone signal network 102 has connected to it a plurality of service switching devices (SSP: Service Switching Point) 103 which execute fundamental switching processing and respective SSPs 103 accommodate therein subscriber terminals 104 (104-1, . . . , 104-n). The SSP 103 only executes the switching operation which is the fundamental function of the switchboard.
With regard to the conventional system of FIG. 1, a call number is used during connection of a call. In other words, the actual assignment of a call number to an incoming call (original call) or to an outgoing call (terminating call) is a conventional technique. For example, in a configuration in which an SSP accommodates subscriber A and B, and in the case that a call between the subscriber A and B is established when subscriber A originates a call and subscriber B terminates the call, two call numbers are created by the SSP, and one call number is assigned to the incoming call from the subscriber A, and the other is assigned to the outgoing call to the subscriber B.
A service key is the information which defines the service application program to be executed in an SCP. The service key is generated in the SSP on receiving a request for providing a communication service from a subscriber terminal.
Next described is a switching method by which a subscriber terminal A accommodated in the SSP 103-1 calls a subscriber B accommodated in the SSP 103-n.
Initially, the SSP 103-1 detects the outgoing call from the subscriber terminal A. Then, the SSP 103-1 asks the SCP 101 what kind of operation it should execute. In response to this inquiry, the SCP 101 asks the SSP 103-1 for information. The SSP 103-1 supplies the SCP 101 with a call number of the subscriber terminal A on the calling side and an incoming call number of the subscriber terminal B on the reception side. The SCP 101 receives this information and issues an instruction to the SSP 103-1 so as to establish the path formed by the subscriber terminal A, the SSP 103-1 and the telephone signal network 102. The SSP 103-1 then establishes this path in response to the instruction.
When the SSP 103-1 transmits to the SCP 101 a signal indicating that the path has been established, the SCP 101 checks the position of the subscriber terminal B and transmits a connection request instruction to the subscriber terminal B to the SSP 103-n. When it receives this instruction, the SSP 103-n checks the "idle" and/or "busy" condition of the subscriber terminal B and transmits the checked condition to the SCP 101. If the subscriber terminal B is not in the communication condition (which means subscriber terminal B is in the idle condition), then the SCP 101 transmits to the SSP 103-n an instruction to establish a path formed by the telephone signal network 102, the SSP 103-n, and the subscriber terminal B. The SSP 103-n receives this instruction, establishes the path and then transmits a path establishment completion signal to the SCP 101. The SCP 101 receives this path establishment completion signal and transmits a communication start instruction to the SSP 103-1. This processing enables communication between the subscriber terminal A and the subscriber terminal B.
If, on the other hand, the line of the subscriber terminal B is occupied, then the SCP 101 transmits information indicating the fact that the subscriber terminal B is in a communication condition (i.e. "busy" condition) to the SSP 103-1 through the telephone signal network 102. Then, the SSP 103-1 transmits this information to the subscriber terminal A and generates a busy signal.
This method, however, has a problem because many exchanges of control information are required between the SSP 103 and the SCP 101.
In an intelligent network, an SSP having a switchboard function is utilized simply as a switching machine and the whole service control is effected by the SCP. This has the advantage that, when the service is added or varied, only the SCP must be varied. However, the exchange of control information needs a lot of time, thus unavoidably increasing the delay time when the service is brought to the subscriber terminal. Even in the most simple processing in which the subscriber terminal A and the subscriber terminal B are connected, as earlier noted in the paragraph on the conventional system, several exchanges of control signals are required between the SCP 101 and the SSP 103. Accordingly, if the service is complicated, then the number of control information exchanges becomes very large. Thus, a complicated service cannot be brought to the subscriber terminal in actual practice.